Uninterruptable ADS-B system for aircraft tracking

ABSTRACT

An aircraft surveillance system that includes an uninterruptible aircraft information broadcasting system (such as an ADS-B system) for transmitting flight information from an aircraft, and one or more ground stations for receiving the broadcast flight information. The flight information preferably includes the aircraft&#39;s aircraft ID, current three-dimensional position, and intended path. Optional components according to the invention include a system and method for validating messages received from the aircraft, and an alternative system and method for determining the aircraft&#39;s position if a primary navigation aid, such as GPS, is not available. In one embodiment of the invention, the system includes a transmitter and an uninterruptible power supply that are disposed within a secure housing within the aircraft. This serves to prevent passengers and crew members from disabling the system.

CROSS REFERENCE TO RELATED APPLICATION

[0001] This application claims the benefit of U.S. ProvisionalApplication Serial No. 60/324,169, which was filed Sep. 21, 2001 andentitled “Uninterruptible ADS-B System for Aircraft Tracking”, and whichis incorporated herein by reference.

FIELD OF THE INVENTION

[0002] This invention relates generally to aircraft surveillancesystems, and more particularly to secure aircraft surveillance systemsthat are configured for alerting air traffic controllers if an aircraftdeparts substantially from an expected flight path or pattern ofbehavior.

BACKGROUND OF THE INVENTION

[0003] The terrorist hijacking and suicide crashes of four U.S. civilianairliners on Sep. 11, 2001, were tragic and unforeseen. The inability ofthe air traffic control and civil defense infrastructure to respondeffectively to the situation as it developed was due, in part, tolimitations of the current radar-based surveillance infrastructure.

[0004] Because of timing delays and accuracy limitations inherent in thedesign of current radar-based air traffic control systems, controllersare unable to determine the real-time intent of aircraft they aretracking. Moreover, current radar surveillance systems depend ontransponder responses from the aircraft to operate at maximumefficiency. The September 11 terrorists disabled or turned off someaircraft transponders in the cockpit of the hijacked aircraft, making itdifficult to track the aircraft. This, combined with the limitations ofcurrent surveillance radar systems, made it nearly impossible forcontrollers to realize that three of the aircraft had turned intocollision courses with ground targets.

[0005] Thus, there is a need for an aircraft surveillance system thatcannot be interrupted by unauthorized persons. There is a further needfor an improved surveillance system that is configured to warn groundcontrollers when an aircraft acts outside of cleared parameters.Furthermore, there is a need for systems that alert ground controllersif someone in the aircraft is attempting to send a false signal todeceive the controllers into believing that the aircraft is following aplanned course when in fact it has been diverted. In addition, there isa need for an improved surveillance system that allows pilots to quicklyand reliably issue a distress signal upon realizing that their aircraftis in danger of being hijacked.

SUMMARY OF THE INVENTION

[0006] The present invention meets the objectives set forth above byproviding an on-board broadcast surveillance system and method thatcannot be interrupted and that provides three-dimensional positioninformation to ground or airborne controllers via a data transmitter.Optionally, the broadcast information may include the Ownship aircraft'saircraft ID and intended path. Other optional components according tothe invention include a system and method for validating messagesreceived from the aircraft, and an alternative system and method fordetermining the aircraft's position if a primary navigation aid, such asthe Global Positioning System (“GPS”), is not available.

[0007] In a preferred embodiment, the invention equips an aircraft witha small uninterruptible Universal Access Transceiver/Automatic DependentSurveillance—Broadcast (“UAT/ADS-B”) transmitter (or other suitabletransmitter) that is capable of broadcasting aircraft ID,three-dimensional position and aircraft intent. The device contains aninternal GPS receiver to determine aircraft position and has anuninterruptible power supply that can not be disabled from the cockpit.The device, which is preferably located in the aircraft's equipment bay,automatically begins broadcasting aircraft position, ID and intent themoment the aircraft is powered up and continues to broadcast thatinformation, in real-time, until the aircraft is on the ground and shutdown. Via an optional external interface, the device may receive andbroadcast flight plan information from the on-board flight managementcomputer. Such information is then made available for comparison tooriginally filed ATC flight plan data. This allows air traffic control(“ATC”) authorities to detect any inappropriate changes to theaircraft's intended destination shortly after the changes are enteredinto the aircraft's flight management computer.

[0008] The invention may further provide a ground infrastructure thatpreferably comprises a plurality of receivers for receiving theinformation transmitted from the aircraft. Preferably, about 600low-cost UAT ADS-B receivers would be located throughout the continentalUnited States to provide full CONUS real-time surveillance. The systemwould be equipped with the capability of determining whether theequipped aircraft were flying within the “normal” parameters of itsflight plan. Upon detecting a deviation from the flight plan, the systemwould provide controllers and civil defense authorities with animmediate alert. If an aircraft deviated from its flight plan, its ADS-Bsignal would continue to provide real-time position, altitude, headingand intent of the aircraft to air traffic control and civil defenseauthorities. Airborne controller stations may optionally replace some orall ground controller stations.

[0009] A system and method for validating messages received from theaircraft may be based on the ability of the UAT to perform rangemeasurements based on signal propagation time, giving rise to severaladvantages. More specifically, the system can determine whether theaircraft's reported position (i.e., the position transmitted by theaircraft) is valid by comparing a range that corresponds to the target'sreported position with a range derived from signal propagation times. Asan additional validity check, or if GPS service is unavailable, theposition of a particular aircraft can be determined by receiving atleast a partial State Vector (identity plus altitude) at multiplecontroller stations, and then using time of reception differentialsamong a network of such stations to compute lines of position.

[0010] Additional anti-spoofing can be accomplished by validating thelast received position information with a dead reckoning algorithm. Whenimplementing this functionality, any jumps in speed and velocity outsidea preset limit are rejected.

[0011] In the event that GPS position information becomes unavailable, adead reckoning function can be used to estimate the aircraft's position.Inexpensive inputs such as heading from a magnetic flux gate, changes invelocity from a solid state accelerometer, and altitude from an optionalself-contained barometer can also be used to enhance the dead reckoningcalculation. As will be understood by one skilled in the art, thisself-contained barometer is optional because the aircraft is preferablyequipped with an altimeter that is not affected by any loss of GPSposition information.

[0012] The invention may further include a panic button within thecockpit of the aircraft that, when activated, transmits a signal to anaircraft information broadcasting system indicating that the Ownshipaircraft is in danger of being hijacked. The aircraft informationbroadcasting system then immediately transmits a signal that triggers anappropriate alarm at a ground station. This aspect of the system isadvantageous because it allows pilots to issue a distress signal withouthaving to enter a complex code. Also, in a preferred embodiment of theinvention, the aircraft information broadcasting system is preferablytamper-proof and located outside the aircraft's cockpit. As a result, itis unlikely that a hijacker would be able to disable the aircraftinformation broadcasting system before the pilot transmits a distresssignal to air traffic control.

[0013] More particularly, a system according to a preferred embodimentof the invention comprises a housing defining an interior portion and anaircraft information broadcasting system that is disposed within theinterior portion of the housing. In this embodiment of the invention,the system is configured for broadcasting flight-related informationthat is related to the Ownship aircraft's current flight. The housing isconfigured for restricting access to the aircraft informationbroadcasting system while the aircraft is in flight.

[0014] In one embodiment of the invention, the system is configured forbroadcasting the flight-related information in real time and in asubstantially continuous manner while the aircraft is in flight. In aparticular embodiment of the invention, the flight-related informationincludes one or more of the following: (1) the aircraft's current flightID, (2) the current three-dimensional position of the aircraft, (3) theaircraft's current velocity, (4) waypoint information for the aircraft;and (5) the aircraft's current intent information.

[0015] In another embodiment of the invention, the system's housingcomprises a robust material that substantially surrounds the aircraftinformation broadcasting system and that thereby restricts access to theaircraft information broadcasting system. In a particular embodiment ofthe invention, this housing is configured to be locked while theaircraft is in flight. In one embodiment of the invention, the housingand the aircraft information broadcasting system are configured forbeing disposed within a portion of the aircraft that is outside of theaircraft's cockpit while the aircraft is in flight. The aircraftinformation broadcasting system is preferably located within theaircraft's equipment bay.

[0016] In yet another embodiment of the invention, the system comprisesan information reception and analysis station that is configured forcomparing intent information that is broadcast from the aircraft'saircraft information broadcasting system with approved flight pathinformation to determine whether the aircraft is being directed towardan improper destination. In this embodiment of the invention, the systemis preferably configured for generating an alarm if the intentinformation differs from the approved flight path information by morethan a predetermined amount.

[0017] In a further embodiment of the invention, the system comprises aninformation reception and analysis station that is configured tovalidate information received from the aircraft information broadcastingsystem using triangulation techniques. Similarly, the system ispreferably configured for generating an alarm if one or more measuredaspects of the aircraft's current flight differs from the expected ormeasured flight characteristics of the aircraft.

[0018] An additional embodiment of the invention comprises a method ofbroadcasting information related to an aircraft. This method comprisesthe steps of: (1) providing a housing that defines an interior portionand that is configured for restricting access to the housing's interiorportion while the aircraft is in flight; (2) providing an aircraftinformation broadcasting system that is configured for broadcastingflight-related information from the aircraft; (3) positioning theaircraft information broadcasting system within the interior portion ofthe housing; and (4) using the aircraft information broadcasting systemto broadcast the flight-related information from the aircraft while theaircraft information broadcasting system is disposed within the interiorportion of the housing and while the housing is restricting access tothe interior portion.

[0019] Yet another embodiment of the invention comprises a method oftracking an aircraft. This method comprises the step of providing anaircraft with an information broadcasting system that is configured forbroadcasting information related to a current flight of the aircraft ina substantially uninterruptible manner while the aircraft is in flight.

[0020] The invention described above is expressed in terms of systemsand methods that are configured for executing, or that include, varioussteps. However, it will be understood by one skilled in the art that theinvention also includes systems that are configured to perform, andcomputer-readable media that include computer-executable instructionsfor executing, the steps included within the above-described methods.Similarly, one skilled in the art will understand that the inventionalso includes methods that include, and computer-readable media thatinclude computer-executable instructions for executing, the stepsexecuted by the above-described systems.

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Having thus described the invention in general terms, referencewill now be made to the accompanying drawings, which are not necessarilydrawn to scale, and wherein:

[0022]FIG. 1 is a block diagram of an aircraft information broadcastingsystem according to a preferred embodiment of the present invention.This figure depicts the interface between the aircraft informationbroadcasting system and various external sources of information.

[0023]FIG. 2 is a block diagram of an aircraft surveillance systemaccording to a preferred embodiment of the invention.

[0024]FIGS. 3A and 3B depict a flowchart that generally illustrates asurveillance module according to the current invention.

[0025]FIG. 4 depicts a flowchart that generally illustrates an aircraftinformation analysis module according to the current invention.

[0026]FIG. 5 is a block diagram of an aircraft information broadcastingsystem according to an alternative embodiment of the present invention.Like FIG. 1, this figure depicts the interface between the aircraftinformation broadcasting system and various external sources ofinformation.

DETAILED DESCRIPTION OF THE INVENTION

[0027] The present invention now will be described more fullyhereinafter with reference to the accompanying drawings, in whichpreferred embodiments of the invention are shown. This invention may,however, be embodied in many different forms and should not be construedas limited to the embodiments set forth herein. Rather, theseembodiments are provided so that this disclosure will be thorough andcomplete, and will fully convey the scope of the invention to thoseskilled in the art. Like numbers refer to like elements throughout.

[0028] Overview

[0029] The present invention provides an aircraft surveillance systemthat allows air traffic control and civil defense to track aircraft. Inone embodiment of the invention, the system continuously transmitsaircraft flight information to a computer (e.g., a ground-based “groundcomputer”) that compares current flight information with approvedclearances. In a preferred embodiment of the invention, the systemtransmits this flight information in ADS-B format based on GPS positioninformation. If the flight characteristics of the Ownship aircraft areoutside of approved clearances, the system issues an alert to airtraffic control and civil defense authorities, which can then actquickly to prevent the aircraft from being used for destructivepurposes. As discussed in more detail below, one embodiment of thissystem is tamper-proof and is positioned in the equipment bay of theaircraft so that potential hijackers can not shut down or otherwisehinder the operation of the aircraft surveillance system. The systemalso preferably includes anti-spoofing functionality, and the capabilityto function even when GPS service is unavailable. The structure andoperation of the system are discussed in greater detail below.

[0030] General Structure of the Aircraft Surveillance System

[0031] In one embodiment of invention, an Ownship Aircraft 95, shown inFIG. 2, is outfitted with a small, robust aircraft informationbroadcasting system 10 that is configured for continuously transmittingaircraft flight information, preferably in real-time, while the aircraftis in flight. As shown in FIG. 1, this aircraft information broadcastingsystem 10 preferably comprises a power source 20, an external interface30, an internal WAAS GPS Engine 40, a UAT Transmitter 50, and an ADS-Bprocessor 5. These components are preferably housed within a sturdy,tamperproof housing 12 (such as a steel or strong plastic housing) thatmay be locked during flight to prevent hijackers from tampering with theaircraft information broadcasting system 10. In addition, as shown inFIG. 2, the aircraft information broadcasting system 10 is preferablystored within the equipment bay 15 of the Ownship aircraft 95 so thatthe aircraft information broadcasting system 10 may not easily beaccessed during flight. The structure and functionality of the powersource 20, external interface 30, internal GPS Engine 40, UATTransmitter 50, and ADS-B Processor 5 are discussed in greater detailbelow.

[0032] The Power Source

[0033] To prevent hijackers from disabling the aircraft informationbroadcasting system 10 during flight, the aircraft informationbroadcasting system 10 is preferably equipped with a backup power source20 that is independent of the aircraft information broadcasting system's10 primary power source (which is not shown and which may be, forexample, the aircraft's power bus). In a preferred embodiment of theinvention, this backup power source 20 is a rechargeable battery that isautomatically charged by the aircraft's primary power source. Thisallows the aircraft information broadcasting system 10 to operatewithout interruption even if power is no longer available from theaircraft information broadcasting system's primary power source.

[0034] The External Interface

[0035] As may be understood from FIG. 1, the aircraft informationbroadcasting system 10 is equipped with an external interface 30 forreceiving information from various optional external navigationalcomponents within the Ownship aircraft. For example, in one embodimentof the invention, the external interface 30 is connected to the Ownshipaircraft's altimeter 60, flight management computer 70, and controlpanel 80. In a particular embodiment of the invention, the aircraft'saltimeter 60, flight management computer 70, and control panel 80 areall located in the Ownship aircraft's cockpit 90, and the externalinterface 30 is located outside of the aircraft's cockpit 90. Forexample, in one embodiment of the invention, the external interface 30is located in a sturdy, tamperproof housing 12 within the Ownshipaircraft's equipment bay 15. As is discussed in greater detail below,the external interface 30 is configured to receive information regardingthe Ownship aircraft's altitude from the altimeter 60, informationregarding the Ownship's aircraft's flight path and flight plan from theFlight Management Computer 70, and the Ownship aircraft's current flightID and UAT configuration from the control panel 80.

[0036] GPS Engine

[0037] The aircraft information broadcasting system 10 further includesan internal GPS Engine 40, such as a Wide Area Augmentation System(WAAS) GPS Engine. This allows the aircraft information broadcastingsystem 10 to determine the latitude and longitude of the Ownshipaircraft. In the alternative, the GPS Engine can be used to determinethe altitude and three-dimensional position of the Ownship aircraftindependently of other instrumentation within the Ownship aircraft.

[0038] Transmitter

[0039] As may be understood from FIG. 1, the aircraft informationbroadcasting system 10 includes a transmitter, such as a UAT Transmitter50, for transmitting ADS-B information from the aircraft informationbroadcasting system 10 to various ground stations 100 or aircraft. Suchinformation may include, for example, the Ownship aircraft's locationinformation, altitude information, velocity information, waypointinformation and intended course information.

[0040] ADS-B Processor

[0041] The ADS-B Processor (e.g., a LDPU Series ADS-B link and displayprocessing unit from UPS Aviation Technologies) includes computerhardware and software, along with interfaces to the other components ofthe aircraft information broadcasting system 10. The ADS-B Processorimplements necessary communication and control tasks that are performedby the ADS-B system.

[0042] Additional Components

[0043] In addition to the aircraft information broadcasting systemdescribed above, the Aircraft Surveillance System preferably comprisesat least one ground station (GBT) 100 for receiving ADS-B signals fromthe aircraft information broadcasting system 10. As may be understoodfrom FIG. 2, each ground station 100 is preferably connected to a groundcomputer 102, which is connected to the Air Traffic Control (ATC)computer network 104. Accordingly, the ground computer 102 is configuredto receive ADS-B information from the Ownship aircraft via the GBT 100.As discussed in greater detail below, the ground computer 102 is furtherconfigured for receiving the Ownship's ATC approved clearances from theATC network 104 and for automatically determining whether the Ownshipaircraft has diverged substantially from the ATC approved clearances.For the purposes of this application, an “information reception andanalysis station” may comprise at least one ground station 100 and atleast one ground computer 102.

[0044] Applicable Technology

[0045] Technology for use in implementing the aircraft informationbroadcasting system 10 is available from multiple vendors including UPSAviation Technologies, Inc. of Salem, Oreg., namely: (1) ADS-B link anddisplay processing unit (LDPU) Model AT9000; (2) ADS-B ground basedtransceiver Model GBT2000; and (3) Model UAT Datalink. Similarly,various components for use in this system are described generally in thefollowing U.S. patents and patent applications, which are incorporatedherein by reference: (1) U.S. Pat. No. 5,493,309 to Bjornholt, whichissued on Feb. 20, 1991; and (2) published U.S. patent application20020032528 to Lai, which was filed on Mar. 14, 2002.

[0046] Functionality of the Aircraft Surveillance System

[0047] In a preferred embodiment of the invention, the aircraftsurveillance system continuously executes a surveillance module 200while the Ownship aircraft 95 is airborne. As may be understood fromFIG. 3, when executing the surveillance module 200, the systempreferably first transmits, at step 210, intended course and relatedinformation (sometimes referred to as “intent”) from the Ownshipaircraft's flight management computer 70 to the aircraft informationbroadcasting system 10. Next, at step 220, the system optionallytransmits UAT Control Information from the Control Panel 80 to theaircraft information broadcasting system 10. The system then proceeds toStep 230, where it transmits the altitude of the Ownship aircraft 95from the altimeter 60 to the aircraft information broadcasting system10. The system then advances to Step 240 where it uses the internal GPSengine 40 to determine the location, velocity, and (optionally) thealtitude of the Ownship aircraft 95. As will be understood by one ofordinary skill in the art, while steps 210-240 above are described asoccurring in a particular sequence, these steps may be executed in anyother order or at the same time. Furthermore, one or more of Steps210-230 may optionally be excluded from the surveillance module 200.This may be done, for example, in an embodiment of the invention inwhich the aircraft information broadcasting system 10 is autonomous inthat it does not receive information from other aircraft control systemssuch as an altimeter 60, flight management computer 70, or control panel80.

[0048] After completing steps 210-240, the system proceeds to step 250where it uses the UAT transmitter 50 to transmit the Ownship aircraft'saltitude information, location information, velocity information,waypoint information and intended course information from the aircraftinformation broadcasting system 10 to the GBT 100. The system thentransmits, at Step 260, the altitude information, location information,velocity information, waypoint information and intended courseinformation from the GBT 100 to the Ground Computer 102. The system thenadvances to Step 270 where it uses the ground computer 102 to executethe Aircraft Information Analysis Module 300. The system then repeatsSteps 210 through 270. In one embodiment of the invention, the systemrepeats Steps 210 through 270 substantially continuously while theOwnship aircraft 95 is in flight.

[0049] It should be understood that other embodiments of the inventionmay be configured to transmit greater or fewer items of information fromthe aircraft information broadcasting system 10 to the GBT 100 thandetailed above. For example, in one embodiment of the invention, thesystem is only configured to transmit altitude information, locationinformation, velocity information, and waypoint information from the GBT100 to the Ground Computer 102.

[0050] As may be understood from FIG. 4, when executing the aircraftinformation analysis module 300, the system first executes step 310where the ground computer 102 receives, from the ATC Computer Network104, the ATC approved clearances that correspond to the Ownshipaircraft's flight ID. Next, at step 320, the ground computer 102compares the altitude, location, velocity, waypoint and intended courseinformation that was received from the GBT 100 with the ATC approvedclearances that correspond to the Ownship aircraft's flight ID. At step330, the ground computer 102 then determines whether the altitude,location, velocity, waypoint, and intended course information that wasreceived from the GBT 100 are each within a predetermined safety marginof the ATC approved clearances for the Ownship's current flight. If so,the system proceeds to Step 350 where it completes execution of theAircraft Information Analysis Module 300. If not, the system proceeds toStep 340 where it issues an alarm indicating that the informationtransmitted from the Ownship aircraft does not comport with approvedclearances. For example, the system may issue an alarm by sending anelectronic message from the ground computer 102 to an air trafficcontroller or to a civil defense authority. Military aircraft can beequipped with a monitor that displays information that has beentransmitted from the aircraft information broadcasting system 10 or theGBT 100. This information can help the pilots of the military aircrafttrack the Ownship aircraft 95.

[0051] Returning for a moment to Step 330, the safety margin for thevarious parameters received by the GBT is preferably chosen to minimizethe occurrence of false alarms, and also to assure that the systemdetects any improper divergence from the ATC approved clearances earlyenough to take proper action. The system is preferably configured toallow a user to specify a different safety margin for each parameter.For example, the user may specify that if the Ownship aircraft's actualaltitude is not within 5% of the approved altitude, the system shouldissue an alarm. Similarly, the user may specify that if the Ownshipaircraft's actual velocity is not within 4% of the approved velocity,the system should issue an alarm. By the same token, the user mayspecify that if the intended course of the aircraft is substantiallydifferent from the ATC approved clearances, the system should issue analarm. For example, the system is preferably configured to issue analarm in response to the intended course of the aircraft and the ATCapproved clearances differing by a pre-determined margin. In oneembodiment of the invention, the system is configured to issue an alarmin response to the intended course of the aircraft differing from theaircraft's approved course by more than a predetermined number ofnautical miles (e.g., 5 nautical miles).

[0052] A tracking file built in the ground computer 102 or the ATCnetwork 104 can be used to predict a probable subsequent position andvelocity for the aircraft. This predicted subsequent position andvelocity may be compared to the position and velocity informationreceived from the aircraft. If the predicted position and/or velocitydiffer from the received position and velocity information by more thana specified amount, the system preferably issues an alarm in the mannerdiscussed above, or in any other suitable manner known in the art.

[0053] It should be understood that the modules executed by the groundcomputer 102 may alternatively be programmed into a computer within theATC network 104.

[0054] Anti-Spoofing Features

[0055] In view of the fact that terrorists are becoming increasinglysophisticated in their methods of hijacking aircraft, it is useful toprovide a system with anti-spoofing features. Such anti-spoofingfeatures may be used, for example, to detect the presence of a falseADS-B signal that hijackers might transmit from a hijacked aircraft todeceive the system into perceiving that the aircraft is flying accordingto its approved flight plan when it is actually flying off course. Onesuch anti-spoofing feature is based on the ability of ground-basedsystems to use well-known techniques based on signal propagation timesto derive the distance between a particular ground station 100 and theUAT/ADS-B transmitter 50 within the aircraft information broadcastingsystem 10. The system may then compare this calculated “range value”with a range value that corresponds to the distance from the groundstation to the Ownship's reported position. If these two range values donot agree within a predetermined safety factor, the system issues anappropriate alarm. This alarm may be used to alert the authorities thatan false ADS-B signal is being transmitted from the aircraft.

[0056] As an additional validity check, the actual position of theOwnship aircraft 95 can be determined using well-known triangulationtechniques, provided that multiple ground stations 100 receive at leasta partial State Vector (identity plus altitude) of the Ownship aircraft95. The Ownship aircraft's triangulated position can then be comparedwith the position that is transmitted from the Ownship aircraft 95 to aground station 100 via the UAT transmitter. If these two position valuesdo not agree within a predetermined safety factor, the system issues anappropriate alarm. This alarm may be used to alert the properauthorities that a false ADS-B signal is being transmitted from theaircraft.

[0057] As a further validity check, the actual position of the Ownshipaircraft 95 can be calculated using well-known dead reckoningalgorithms. This calculated position is then compared with the positionthat is transmitted from the Ownship aircraft 95 to a ground station 100via the UAT transmitter. If these two position values do not agreewithin a predetermined safety factor, the system issues an appropriatealarm. This alarm may be used to alert the proper authorities that afalse ADS-B signal is being transmitted from the aircraft.

[0058] Position Loss Considerations

[0059] In the event that the internal GPS engine 40 becomes unable togenerate position information, the position of the Ownship aircraft 95can be determined using well-known triangulation techniques, providedthat multiple ground stations 100 receive at least a partial StateVector (identity plus altitude) of the Ownship aircraft 95.Alternatively, the system may use well-known dead-reckoning techniquesto estimate the position of the Ownship aircraft 95. As shown in FIG. 5,the aircraft information broadcasting system 10 may include inexpensivemeasurement devices such as a magnetic flux gate 410, a solid stateaccelerometer 420, and a self-contained barometer 430 to assist inmaking such dead-reckoning calculations. These dead-reckoningcalculations may also be used in Step 330 above to determine whethervarious system parameters are within pre-determined safety margins ofthe ATC approved clearances for the flight.

[0060] Panic Button

[0061] Prior art systems allow pilots to enter a particular code withinthe aircraft navigation system to indicate that the aircraft is indanger of being hijacked. However, hijackers are often able to stoppilots from entering the code, or disable this functionality before analert is sent to air traffic control. To solve this problem, the presentsystem preferably includes a panic button within the cockpit of theaircraft that transmits a signal to the aircraft informationbroadcasting system 10 indicating that the Ownship aircraft 95 is indanger of being hijacked. The aircraft information broadcasting system10 then immediately transmits a signal that triggers an appropriatealarm at the ground station 100. This aspect of the system isadvantageous because it allows pilots to issue a distress signal withouthaving to enter any sort of code, and because, due to the fact that theaircraft information broadcasting system is tamper-proof and preferablylocated outside of the aircraft's cockpit 90, it is unlikely that ahijacker would be able to disable the aircraft information broadcastingsystem before the pilot transmits a distress signal to air trafficcontrol.

[0062] Ground Station Technical Considerations

[0063] The number of ground stations 100 needed for proper surveillancecoverage may vary based upon the desired low altitude threshold forcoverage. This is because line-of-site communication is required betweenthe aircraft information broadcasting system 10 and the ground stations100 that are receiving signals from the Surveillance Unit 10. Thefollowing chart gives some typical values for range vs. altitude.Altitude (AGL, feet) Range (nmi) 1,000 40 5,000 85 10,000 120 15,000 150

[0064] Based on the above chart, if coverage down to 1,000 feet aboveground level (AGL) is desired, a ground station 100 would need to beinstalled every 40 to 80 miles, depending on how much overlap is desiredto support the anti-spoofing and position-loss functionality describedabove. Assuming that every ground station 100 can cover a 40 nmi radiusarea on average, each base station site can provide surveillance over a5,000 square mile area. With approximately 3.0 million square miles inthe continental United States, approximately 600 ground station siteswould be needed to cover the entire continental United States.

[0065] One embodiment of the invention comprises a hexagonal “cellular”grid of ground stations 100, spaced 100 nmi apart. This is estimated togive coverage down to 3,000 feet AGL. In this embodiment of theinvention, each ground station 100 provides coverage over a 70 nmiradius, or 15,000 square miles. As will be understood by one skilled inthe relevant technical field, the exact configuration of these groundstations 100 is determined taking into account various terrain-specificfactors such as terrain blockages.

[0066] It should be understood that controller functions, the GBT 100,ground computer 102, and computers within the ATC computer network 104may alternatively be airborne. For example, these components may belocated within an AWACS aircraft rather than on the ground.

[0067] Conclusion

[0068] Many modifications and other embodiments of the invention willcome to mind to one skilled in the art to which this invention pertainshaving the benefit of the teachings presented in the foregoingdescriptions and the associated drawings. For example, it should beunderstood that, while the system is described as being to configured totransmit the Ownship aircraft's flight-related information in ADS-Bformat, the system may be configured to transmit this information in anyother format known in the art. Accordingly, it should be understood thatthe invention is not to be limited to the specific embodiments disclosedand that modifications and other embodiments are intended to be includedwithin the scope of the appended claims. Although specific terms areemployed herein, they are used in a generic and descriptive sense onlyand not for purposes of limitation.

What I claim is:
 1. An aircraft surveillance system for broadcastinginformation related to an aircraft, said aircraft surveillance systemcomprising: a housing defining an interior portion; and an aircraftinformation broadcasting system disposed within said interior portion ofsaid housing, said aircraft information broadcasting system beingconfigured for broadcasting flight-related information from saidaircraft while said aircraft is in flight, said flight-relatedinformation being related to a current flight of said aircraft, and saidhousing being configured for restricting access to said aircraftinformation broadcasting system while said aircraft is in flight.
 2. Theaircraft surveillance system of claim 1, wherein said aircraftinformation broadcasting system is configured for broadcasting saidflight-related information in a substantially continuous manner whilesaid aircraft is in flight.
 3. The aircraft surveillance system of claim2, wherein said aircraft information broadcasting system is configuredfor broadcasting said flight-related information in real time.
 4. Theaircraft surveillance system of claim 2, wherein said flight-relatedinformation comprises a current flight ID of said aircraft.
 5. Theaircraft surveillance system of claim 2, wherein said flight-relatedinformation comprises a current three-dimensional position of saidaircraft.
 6. The aircraft surveillance system of claim 2, wherein saidflight-related information comprises a current velocity of saidaircraft.
 7. The aircraft surveillance system of claim 2, wherein saidflight-related information comprises waypoint information for saidaircraft.
 8. The aircraft surveillance system of claim 2, wherein saidflight-related information comprises current intent information for saidaircraft.
 9. The aircraft surveillance system of claim 1, wherein saidhousing comprises a robust material that substantially surrounds saidaircraft information broadcasting system and thereby restricts access tosaid aircraft information broadcasting system.
 10. The aircraftsurveillance system of claim 9, wherein said housing is configured to belocked while said aircraft is in flight.
 11. The aircraft surveillancesystem of claim 1, wherein said housing and said aircraft informationbroadcasting system are configured for being disposed within a portionof said aircraft that is outside of a cockpit of said aircraft whilesaid aircraft is in flight.
 12. The aircraft surveillance system ofclaim 11, wherein said housing and said aircraft informationbroadcasting system are adapted to be mounted for use within anequipment bay of said aircraft.
 13. The aircraft surveillance system ofclaim 1, wherein said aircraft surveillance system further comprises apower supply for providing an independent supply of power to saidaircraft information broadcasting system.
 14. The aircraft surveillancesystem of claim 13, wherein said power supply is disposed within saidhousing.
 15. The aircraft surveillance system of claim 14, wherein saidpower supply is a rechargeable battery.
 16. The aircraft surveillancesystem of claim 13, wherein said power supply is configured to provide asupply of power to said aircraft information broadcasting system, saidpower supply being configured to not be interrupted while said aircraftis airborne.
 17. The aircraft surveillance system of claim 1, furthercomprising a GPS receiver that is positioned to be inaccessible by thepassengers and crew of said aircraft while said aircraft is in flight.18. The aircraft surveillance system of claim 17, wherein: said GPSreceiver is disposed within said housing; and said housing is configuredfor restricting access to said GPS receiver while said aircraft is inflight.
 19. The aircraft surveillance system of claim 1, wherein saidaircraft information broadcasting system comprises an ADS-B transmitter.20. The aircraft surveillance system of claim 1, wherein said aircraftinformation broadcasting system includes an external interface forreceiving flight plan information from a flight management computer ofsaid aircraft.
 21. The aircraft surveillance system of claim 1, whereinsaid aircraft information broadcasting system further comprises amagnetic flux gate, an accelerometer, and a barometer.
 22. The aircraftsurveillance system of claim 1 further comprising a ground station thatis configured for receiving said flight-related information.
 23. Theaircraft surveillance system of claim 22, wherein: said flight-relatedinformation includes intent information for said aircraft; and saidaircraft surveillance system comprises an information reception andanalysis station that is configured for comparing said intentinformation with approved flight path information for said aircraft todetermine whether said aircraft is being directed toward an improperdestination.
 24. The aircraft surveillance system of claim 23, whereinsaid information reception and analysis station is configured forreceiving said approved flight path information from one or more airtraffic control computers.
 25. The aircraft surveillance system of claim23, wherein said aircraft surveillance system is configured forgenerating an alarm if said intent information differs from saidapproved flight path information by more than a predetermined amount.26. The aircraft surveillance system of claim 22, wherein: saidflight-related information includes a current three-dimensional positionof said aircraft; said aircraft surveillance system comprises aninformation reception and analysis station that is configured forcomparing said current three-dimensional position with approved flightpath information to determine whether said aircraft is being directedtoward an improper destination.
 27. The aircraft surveillance system ofclaim 26, wherein said aircraft surveillance system is configured forgenerating an alarm if said three-dimensional position informationdiffers by more than a predetermined amount from a predictedthree-dimensional position that is based upon said approved flight pathinformation.
 28. The aircraft surveillance system of claim 1, furthercomprising a panic button disposed within said aircraft, and whereinsaid aircraft surveillance system is configured, in response to saidpanic button being selected by a user, to broadcast a signal indicatingthat said aircraft is in danger.
 29. The aircraft surveillance system ofclaim 28, wherein said aircraft information broadcasting system isconfigured, in response to said panic button being selected by a user,to broadcast a signal indicating that said aircraft is in danger. 30.The aircraft surveillance system of claim 1, wherein said aircraftsurveillance system is configured for validating messages received fromsaid aircraft.
 31. The aircraft surveillance system of claim 1, wherein:said aircraft surveillance system comprises an information reception andanalysis station, said information reception and analysis station beingconfigured to validate aircraft information received from said aircraftinformation broadcasting system by determining an estimated range basedon a signal propagation time and comparing said estimated range with acalculated range that is derived from aircraft information received fromsaid aircraft information broadcasting system.
 32. The aircraftsurveillance system of claim 31, wherein said aircraft surveillancesystem is configured for generating an alarm if said estimated rangediffers from said calculated range by more than a predetermined amount.33. The aircraft surveillance system of claim 1, further comprising aninformation reception and analysis station, said information receptionand analysis station being configured to use triangulation techniques tovalidate information received from said aircraft informationbroadcasting system.
 34. The aircraft surveillance system of claim 1,wherein said aircraft surveillance system comprises an informationreception and analysis station, said information reception and analysisstation being configured for using a dead-reckoning algorithm tovalidate a signal which is represented as corresponding to a particularthree-dimensional position of said aircraft, said signal being receivedfrom said aircraft information broadcasting system.
 35. The aircraftsurveillance system of claim 34, wherein said information and analysisstation is configured for using a dead-reckoning algorithm to determinewhether said signal is valid by performing the steps of: using adead-reckoning algorithm to estimate a first three-dimensional positionof said aircraft, said first three-dimensional position of said aircraftcorresponding to a first point in time; using a dead-reckoning algorithmto estimate a second three-dimensional position of said aircraft, saidsecond three-dimensional position of said aircraft corresponding to asecond point in time; using said first three-dimensional position andsaid second three-dimensional position to determine an estimated modelvalue for said particular three-dimensional position of said aircraft;and comparing said estimated model value for said particularthree-dimensional position of said aircraft with said particularthree-dimensional position of said aircraft.
 36. The aircraftsurveillance system of claim 35, wherein said information and analysisstation is configured for generating an alarm in response to said modelvalue for said particular three-dimensional position of said aircraftdiffering from said particular three-dimensional position of saidaircraft by more than a predetermined amount.
 37. The aircraftsurveillance system of claim 1, wherein said aircraft surveillancesystem comprises an information reception and analysis station, saidinformation reception and analysis station being configured for using adead-reckoning algorithm to validate a current velocity of saidaircraft, said current velocity being received from said aircraftinformation broadcasting system.
 38. The aircraft surveillance system ofclaim 37, wherein said information and analysis station is configuredfor using said dead-reckoning algorithm to validate a current velocityof said aircraft by performing the steps of: using a dead-reckoningalgorithm to estimate a first three-dimensional position of saidaircraft, said first three-dimensional position of said aircraftcorresponding to a first point in time; using a dead-reckoning algorithmto estimate a second three-dimensional position of said aircraft, saidsecond three-dimensional position of said aircraft corresponding to asecond point in time; using said first three-dimensional position andsaid second three-dimensional position to estimate a projected velocityof said aircraft; and comparing said projected velocity of said aircraftwith a current velocity of said aircraft received from said aircraftinformation broadcasting system.
 39. The aircraft surveillance system ofclaim 38, wherein said step of using a dead-reckoning algorithm tovalidate a current velocity of said aircraft comprises the step ofgenerating an alarm if said projected velocity of said aircraft differsfrom a current velocity of said aircraft received from said aircraftinformation broadcasting system by more than a predetermined amount. 40.An aircraft surveillance system for tracking an aircraft, said aircraftsurveillance system comprising: an aircraft information broadcastingsystem disposed within said aircraft, said aircraft informationbroadcasting system being configured for broadcasting flight-relatedinformation in a substantially uninterruptible manner while saidaircraft is in flight, said flight-related information being related toa current flight of said aircraft.
 41. The aircraft surveillance systemof claim 40, wherein said flight-related information comprises a flightID of said aircraft.
 42. The aircraft surveillance system of claim 40,wherein said flight-related information comprises current intentinformation for said aircraft.
 43. The aircraft surveillance system ofclaim 40, wherein said flight-related information comprises a currentthree-dimensional position of said aircraft.
 44. The aircraftsurveillance system of claim 40, wherein said flight-related informationcomprises a current velocity of said aircraft.
 45. The aircraftsurveillance system of claim 40, wherein said flight-related informationcomprises waypoint information for said aircraft.
 46. The aircraftsurveillance system of claim 45, wherein: said flight-relatedinformation comprises a flight ID of said aircraft; said flight-relatedinformation comprises current intent information for said aircraft; saidflight-related information comprises a current three-dimensionalposition of said aircraft; and said flight-related information comprisesa current velocity of said aircraft.
 47. A method of broadcastinginformation related to an aircraft, said method comprising the steps of:providing a housing defining an interior portion, said housing beingconfigured for restricting access to said interior portion while saidaircraft is in flight; providing an aircraft information broadcastingsystem, said aircraft information broadcasting system being configuredfor broadcasting flight-related information from said aircraft whilesaid aircraft is in flight; positioning said aircraft informationbroadcasting system within said interior portion of said housing; andusing said aircraft information broadcasting system to broadcast saidflight-related information from said aircraft while said aircraftinformation broadcasting system is disposed within said interior portionof said housing and while said housing is restricting access to saidinterior portion.
 48. The method of claim 47, wherein said step of usingsaid aircraft information broadcasting system to broadcast saidflight-related information is performed in a substantially continuousmanner while said aircraft is in flight.
 49. The method of claim 47,wherein said flight-related information comprises a currentthree-dimensional position of the aircraft.
 50. The method of claim 47,wherein said flight-related information comprises a current velocity ofsaid aircraft.
 51. The method of claim 47, wherein said flight-relatedinformation comprises waypoint information for said aircraft.
 52. Themethod of claim 47, wherein said flight-related information comprisessaid aircraft's current intent information.
 53. The method of claim 47,further comprising the step of providing a ground station that isconfigured for receiving said flight-related information.
 54. The methodof claim 47, wherein said flight-related information includes intentinformation for said aircraft, and further comprising the step of:comparing said intent information with approved flight path informationto determine whether said aircraft is being directed toward an improperdestination.
 55. The method of claim 47, wherein said flight-relatedinformation includes a current three-dimensional position of saidaircraft, and further comprising the step of: comparing said currentthree-dimensional position with approved flight path information todetermine whether said aircraft is being directed toward an improperdestination.
 56. The method of claim 55, further comprising the step ofgenerating an alarm, in response to said current three-dimensionalposition differing from a predicted three-dimensional position by morethan a predetermined amount.
 57. The method of claim 47, furthercomprising the steps of: using a dead-reckoning algorithm to estimate afirst three-dimensional position of said aircraft for a first point intime; using a dead-reckoning algorithm to estimate a secondthree-dimensional position of said aircraft for a second point in time;using said first three-dimensional position and said secondthree-dimensional position to estimate a projected velocity of saidaircraft; and comparing said projected velocity of said aircraft with areported current velocity of said aircraft that is received from saidaircraft information broadcasting system.
 58. A method of tracking anaircraft comprising the steps of: providing an aircraft with aninformation broadcasting system, said aircraft information broadcastingsystem being configured for broadcasting information related to acurrent flight of said aircraft in a substantially uninterruptiblemanner while said aircraft is in flight.
 59. The method of claim 58,wherein said flight-related information comprises current intentinformation for said aircraft.
 60. The method of claim 58, wherein saidflight-related information comprises a current three-dimensionalposition of said aircraft.